Walter Tamosaitis and watchdogs believe URS Corp. retaliated over his warning that the radioactive waste facility in Hanford, Wash., had safety issues.

When senior scientist Walter Tamosaitis warned in 2011 about fundamental design flaws at the nation's largest facility to treat radioactive waste in Hanford, Wash., he was assigned to work in a basement room without office furniture or a telephone.

On Wednesday, Tamosaitis, an employee of San Francisco-based URS Corp., was laid off from his job after 44 years with the company.

The concerns that Tamosaitis raised two years ago about the design of the waste treatment plant, a $12.3-billion industrial complex that would turn highly radioactive sludge into glass, were validated by federal investigators. Construction of the plant was halted and the Energy Department is trying to address a wide range of problems with the design.

The Hanford site is the nation's most contaminated property, holding 56 million gallons of highly radioactive sludge in underground tanks, some of which are leaking. The complex sits on a plateau above the Columbia River, which could be threatened if the cleanup fails to contain the tank waste.

Only last June, newly appointed Energy Secretary Ernest J. Moniz met with Tamosaitis near the Hanford site, where the U.S. produced plutonium for the Manhattan Project and thousands of nuclear bombs during the Cold War. The meeting raised Tamosaitis' hopes that the long-standing problems with safety at the project would get high-level attention.

Then two weeks ago, Moniz issued a highly unusual statement that reaffirmed the Energy Department's commitment to safety, saying, "We will pursue a safety culture built on an environment of trust and mutual respect, worker engagement and open communication, an atmosphere that promotes a questioning attitude with effective resolution of reported problems, and continuous learning."

But on Thursday, Tamosaitis, a systems engineer with a doctoral degree who had directed a staff of 100 scientists until he began expressing concerns about safety, said URS officials showed up and ordered him to box up his personal belongings, then escorted him out.

The company said in a statement that as a matter of policy it would not comment on such employee matters, but that it had reduced employment levels due to budgetary constraints.

"URS encourages its employees to raise any concerns about safety, which remains the company's highest priority," the statement said.

But Tom Carpenter, executive director of Hanford Challenge, a watchdog group that assisted a number of whistle-blowers at the federal complex, said the dismissal was "clearly another act of retribution against Walter Tamosaitis."

Tamosaitis was among several Hanford complex managers who raised concerns about the safety culture. The Defense Nuclear Facilities Safety Board, an independent federal agency that oversees the nuclear weapons complex, raised its own concerns about similar issues and in 2011 backed up Tamosaitis' concerns. On Thursday, Tamosaitis, 66, said he was unsure what he would do next.

"I enjoyed working and trying to do something for the country," he said. "They killed my career. It sends a message to everybody else that they shouldn't raise issues. Forty-four years of service, a PhD, a recognized expert in nuclear engineering — none of that mattered."